Dynamic Hysteresis Torque Band for Improving the Performance of Lookup-Table-Based DTC of Induction Machines

The magnitude of hysteresis torque band has a considerable effect on the performance of two-level direct torque control (DTC) of induction machines. The conventional DTC fails at low speed due to the poor flux regulation. In this paper, two dynamic hysteresis torque band (DHTB) strategies for the conventional DTC are proposed to solve this problem by dynamically altering the amplitude of hysteresis torque band based on a flux error range. In this way, the simplicity of DTC algorithm is retained since it only requires a minor modification on its structure. The paper also presents further analysis on flux degradation, particularly the droop in between the flux sectors. In addition, the switching frequency effect of reverse voltage vectors for both DHTB schemes is investigated on the performance of the speed-sensorless DTC drive. The effectiveness of the proposed schemes is confirmed by simulation and experimental validation. Results show a significant enhancement in the flux regulation and dynamic torque response from zero motor speed.